The present invention relates generally to superconductive devices and more particularly to a superconductive switch useful in the operation of a superconductive device.
Superconducting devices have a main superconductive coil assemblage and include, but are not limited to, magnetic resonance imaging (MRI) systems for medical diagnosis, superconductive rotors for electric generators and motors, and magnetic levitation devices for train transportation. Superconductive devices usually employ a superconductive switch to transfer between a persistent superconducting operating mode and a non-persistent superconducting operating mode. Typically a superconductive switch is used to start up superconductive operation of the superconductive device and to purposely run down such superconductive operation.
Known superconductive switches are placed in a cryogenic region of the superconductive device where the operating temperature is less than or equal to the critical temperature of the superconductor material used in the main superconductive coil assemblage of the superconductive device. Such a superconductive switch typically has a superconductive coil portion and an electrical heater portion. The coil wire of the superconductive coil portion is wound in a two-in-hand bifilar manner (i.e., adjacent turns in the same layer of coil wire, or the turns in adjacent layers of coil wire, are wound alternately clockwise and counterclockwise as one travels along and between the two ends of the coil wire) for low inductance and has a heavy grade of electrical insulation for adequate voltage standoff capability to meet the switch's design peak terminal voltage. Activation of the electrical heater portion raises the temperature in the superconductive coil portion above the critical temperature.
Quench protection techniques for superconductive devices include techniques for preventing (or delaying) an impending quench and techniques for preventing (or limiting) harm to the superconductive device that is undergoing a quench. Such harm is from damaging high temperatures and high stresses applied locally to the magnet at the quench site. Known techniques for preventing (or limiting) such harm seek to avoid excessive localized heat energy deposition in the superconducting winding and include using a quench-detection signal (from the electrical center of the main superconductive coil assemblage of the superconductive device) directly supplying an energy dump resistor or directly powering a wide-area electrical heater located near the main superconductive coil assemblage of the superconductive device. Such known techniques take a relatively long time to work.